Optical disk, an optical disk device, and a method of managing defects in an optical disk

ABSTRACT

When optical disk defects are arranged by using non-defective areas in place of defective areas, different criteria are used for detecting the defects, depending on the type of data recorded on the disk. For example, to avoid interruptions of real-time recording, less strict criteria are used when audio or video data is recorded than when computer data is recorded. The criteria themselves may also be recorded on the disk.

This application is a divisional of co-pending application Ser. No.09/368,359, filed on Aug. 5, 1999, the entire contents of which arehereby incorporated by reference and for which priority is claimed under35 U.S.C. §120; and this application claims priority of application Ser.No. 222003/98 filed in Japan on Aug. 5, 1998 under 35 U.S.C. §119.

BACKGROUND OF THE INVENTION

The present invention relates to a method of managing defects in a diskrecording medium, an optical disk device recording data on the opticaldisk using such a defect management method, and an optical disk capableof storing information concerning a defect criteria used for replacing adefective area of disk with a non-defective area.

A very high degree of reliability less than 10⁻¹² at worst is requiredof a disk used for recording computer data. Defect-managing systems havebeen used hitherto to accommodate the reality that defects in recordingsectors which lead to an error are unavoidable, even very rare, in thecurrent disk-manufacturing technique.

Disk mediums are subjected to the defect management for assuring datareliability even when dirt, scratches or degradation due to repetitionof rewriting operation is caused. Primary defects occurring at the timeof manufacture of the disks are found through a certifying processcarried out at the time of initializing disks, and secondary defectsoccurring after being put to use are found through verification carriedout at the time of writing, or the like. Sectors found to have a defectare replaced, using sectors located in a spare area formed on part of adisk other than a user area. In the defect management, a pair of a userarea and a spare area is called a group.

In an example of arrangement of user areas and spare areas on a disk,the data area consists of a single group. However, there are manyoptical disks in which a data area is divided into a plurality ofgroups. When a defective group is found in a group, it is firstattempted to replace the defective sectors using sectors in a spare areaof the same group. In many cases, an optical disk is configured suchthat a recording capacity of a spare area is several % of that of a userarea. The 90 mm magneto-optic disk standard defined by ECMA-154 orECMA-201, and the DVD-RAM standard defined by ECMA-272 are examples ofsuch configuration.

Incidentally ECMA is an abbreviation of European Computer ManufacturersAssociation, DVD is an abbreviation of digital video disk, and RAM is anabbreviation of random-access memory.

The presence or absence of a defect in a sector can be determined by anerror in an ID signal representing a physical address of the sector, anerror in a recorded data signal, or a servo error signal.

When a plurality of ID's are recorded in the header area for eachsector, if not less than a predetermined number of ID's for each sectorcontain an error, the sector in question is found to have a headerdefect. In the DVD-RAM standard for example, each sector is providedwith four ID's, and an error can be detected for each ID. Each sector isfound not to have a header defect if it has not more than two ID errors:a sector having three or more ID errors is found to have a headerdefect, since its reliability is low.

Further, the presence or absence of an error in a recorded data signalis detected by the use of an error correcting code added thereto. Whenmore than a predetermined number of errors are included per unit ofrecording, the data signal is found to have a data defect. The “unit ofrecording” may be a sector or a block constituted of a plurality ofsectors depending on the span of an error correcting code (ECC).

In the DVD-RAM standard, data is recorded in sectors on a disk, and issubjected to error-correcting coding in units of 16 sectors, called anECC block. Data of 32 KB constituting one ECC block is arranged in theform of matrix of 172×192 bytes (or 172 columns×192 rows), andReed-Solomon codes (inner code PI, outer code PO) of 10 bytes and 16bytes are added in column direction and row direction, respectively, toconstitute a product code.

The inner code PI is disposed so as to be completely within a sector. Bymeans of the inner code PI, the number of error bytes in each row of thereproduced data can be determined. In accordance with the detectednumber of errors, reliability of each row is evaluated, and whether eachsector or each block has a data defect can be determined based on thenumber. For instance, a sector including four or more rows having fouror more error bytes is found to have a data defect, or a block includingsix or more such rows are found to have a data defect.

With regard to detection of defects based on a servo error signal, whenthe magnitude of the servo error signal such as a tracking error signalexceeds a predetermined value that makes it difficult to ensure theservo control stability required of data recording, a sector in questionis found to have a servo defect.

When a sector is found to have a header defect, a data defect or a servodefect, it is found to be defective.

Generally, in the defect management, two different methods are used forperforming replacement of a sector. One is a slip replacement, and theother is a linear replacement.

The slip replacement is applied to primary defects. If a defectivesector is found at the time of certifying a disk, the next sector isused in place of the defective sector. In a disk drive device, foraccessing a sector containing data, a logical address is converted intoa physical address representing the position of the sector, and a sectorhaving ID's representing the physical address is accessed. When the slipreplacement has been performed, the physical address numberscorresponding to the logical addresses are shifted, or “slip” by one.

The slip replacement is carried out within each group. For instance, ifthere occur two slip replacements of m sectors and n sectors in a userarea, the end of the user area of the group is shifted into the head ofthe spare area by (m+n) sectors. If such slip replacements are made, thelinking relation between the physical addresses and logical addresses isshifted by the number of replaced sectors for all the sectors succeedingthe replaced sectors. Primary defects subjected to the slip replacementare registered in a PDL (Primary Defect List). The list contains thephysical addresses of defective sectors in each entry.

Linking the physical addresses with the logical addresses can be madeonly when a disk is initialized, and therefore, the slip replacement isapplied to primary defects only.

The linear replacement is applied to secondary defects. When a defectivesector is found, replacement is effected using spare sectors in a sparearea. When an ECC block (formed of 16 sectors) is found to contain adefective sector, the entire ECC block is replaced with 16 sectors in aspare area. There may be a case where a block in a spare area havingreplaced another block is subsequently replaced with another block. Asubstitutive sectors are given the same logical addresses as theoriginal sectors.

The linear replacement is effected within the same group first. Forinstance, when two linear replacements of m blocks and n blocksrespectively occur in a user area, m blocks and n blocks at thebeginning of the unused part of the spare area are used. It may be sodesigned that when the spare area of the same group has been used up thespare area in another group is used. Secondary defects subjected tolinear replacement are registered in an SDL (Secondary Defect List). Thelist contains physical addresses of defective sectors and substitutivesectors in each entry.

When such a linear replacement has been made, every time an access ismade using a logical address which designated a substitutive sector, anaccess to the substitutive sector and subsequent return have to be made.Therefore, the average data transfer rate is substantially lowered whenthe secondary defects exist.

A set of the defect lists PDL and SDL is stored in a defect managementarea within a control information area in each of outer and innerperiphery parts. They are disposed at a plurality of locations, and theyare recorded together with information on the structure of a disk.

Generally, in recording devices, criteria for detecting primary andsecondary defects are set in the following way.

A disk is at its best condition when primary defects are detected andregistered. The number of defects on the disk increases with time orusage due to scratches and dirt, and resultant degradation. Therefore,the primary defects are detected and replacement is effected by using acriteria which is more strict than that for detecting the secondarydefects, so that some additional scratches or dirt will not results inthe finding of a defect according to the criteria for detecting thesecondary defects.

Although the secondary defects are detected with a criteria which isless strict than that for the primary defects, a margin of safety isleft between the criteria for detecting the secondary defects and theerror-correcting capability, so as to ensure error correction duringreproduction. In this way, different criteria are used for the primarydefect detection and the secondary defect detection.

Conventionally, optical disks are used mainly for computer daterecording, and therefore, the primary concern was to improve the datareliability, and defect management mainly consisting of replacementusing spare sectors has been developed to deal with the defects in therecording sectors causing the errors.

In recent years, with increasing capacity of optical disks, their usesare expanding to the video recording field, such as in DVD.

Data files for recording computer data (PC files) are expected to becompletely error-free, and high reliability is required of recording. Incontrast, data files for recording audio or vide data (AV files) requirerecording data inputted continuously in real time. In some cases, errorsare permissible as long as the disturbance of reproduced images orsounds is not noticed, so that data reliability is not required to be ashigh as in computer data recording. Instead, non-interruption ofrecording is important.

That is to say, with regard to storage devices for computer datarecording, primary importance is the reliability rather than recordingtime, while, for storage devices for video recording, primary importanceis continuous recording performance. Consequently, in case of using thesame type of disk for recording both audio or video data and computerdata, it is required to ensure reliability and recording speed whichmeet the requirements of the respective recordings. Likewise, defectmanagement must be adaptable to both types of recording.

Conventional defect management for optical disks has the followingdrawbacks.

For carrying out replacement to deal with secondary defects of a disk atthe time of recording, data is reproduced from the recorded part forverification, and if errors of more than a prescribed criteria, or adefective part from which reproduction is impossible is found, the datarecorded in that part is re-recorded in substitutive sectors in a sparearea, and data is again reproduced from the substitutive sectors forverification. Thus, when a secondary defect is detected, and replacementis effected, the time needed is four times more than the time needed forrecording data once. In case of recording audio or video data in realtime, it is likely that recording is interrupted if a defect isdetected.

One solution to this problem is not to detect secondary defects duringthe recording of audio or video data. In this case, the reproduced imageor the like may have disturbances at parts having the secondary defects,but such disturbances are considered less objectionable thaninterruption of recording. The underlying assumption is that onceprimary defects have been removed at the time of initialization of thedisk, any secondary defects that might occur will be minor. If the scaleof the secondary defects is greater than predicted, the disturbance ofthe reproduced picture may be intolerable, and thus this solution fails.

Where the optical disks are used for recording audio or video data, itis considered unnecessary to detect defects with criteria which is asstrict as that used in recording computer data. This is because, if theexcessively strict criteria is used, sectors which are permissible foraudio or video data are also found defective, and video recording isinterrupted when the time-consuming replacement is effected. Because theconventional defect management method does not take into considerationthe intended use of the optical disk, and the criteria used is of thesame level regardless of the intended use of the optical disk, there wasno conception of using the optimum defect detecting method.

SUMMARY OF THE INVENTION

The present invention has been made overcome the above-outlined problem,and its object is to adapt defect management to the type of datarecorded on an optical disk, or the intended use of the disk.

Another object is to improve the interchangeability of the optical disk.

A further object is to improve the utility of optical disks forrecording audio or video data.

According to a first aspect of the invention, there is provided a methodof managing defects on an optical disk used for recording data,including

determining a criteria for detecting defects according to the type ofdata for which defects are to be detected; and

detecting defects using said criteria when d at a is record ed on orreproduced from the disk.

With the above arrangement, it is possible to use the criteria suitablefor the particular type of data for which defects are to be detected.

The step of detecting defects may be performed with regard to datarecorded on the disk.

In this case the defects may be detected when the data is recorded onthe disk, or when the data is reproduced for verification of the datahaving been recorded. When the defects are detected when the data isrecorded, determination of presence or absence of servo defects andheader defects can be made, but determination of presence or absence ofdata defects cannot be made. When the defects are detected duringreproduction for verification, presence of absence of data defects aswell as servo defects and header defects can be determined.

The step of detecting defects may alternatively be performed when thedata is reproduced. In such a case, if defects are detected, thereproduction of the data is re-tried. Decision on whether thereproduction is to be re-tried is made using different criteriadepending on the type of data being reproduced.

The method may further comprise the step of using non-defective areas ofthe optical disk in place of defective areas of the optical disk.

With the above arrangement, the result of the defect detection can beused in making a decision as to whether the areas found to be defectiveshould be replaced with non-defective areas.

The step of determining a criteria may include:

selecting one of the plurality of criteria according to the type of datafor which defects are to be detected.

With the above arrangement, the defect criteria can be determined simplyby providing a signal which selects one of the plurality of criteriaprovided in advance, rather than specifying the values forming thecriteria.

The plurality of criteria may include at least a first criteria, and asecond criteria, the second criteria being less strict than said firstcriteria, and said step of selecting may include selecting the firstcriteria when the data for which defects are to be detected is one forwhich time restriction with regard to data recording or reproduction isless strict, and selecting the second criteria when the data for whichdefects are to be detected is one for which time restrictions withregard to data recording or reproduction is more strict.

An example of the data for which time restriction with regard to datarecording or reproduction is less strict is computer data. An example ofthe data for which time restriction with regard to data recording orreproduction is more strict is audio or video data.

By using a less strict criteria for the audio or video data,interruption of the audio or video data recording is avoided unless thedefect is of such a degree that the resultant disturbance in the soundor picture is intorerable.

The method may further include sending control information forspecifying the criteria, from means for processing data to be recorded,to means for recording said data.

The above-mentioned means for processing data to be recorded is forexample a host device. The above mentioned means for recording the datais for example a disk device.

With the above configuration, the host device can set criteria which isfinely optimized for the type of the data to be recorded on the disk.

The data may be recorded in units of recording, and the step of sendingcontrol information may send the control information for each unit ofrecording.

With the above configuration, it is possible to dynamically set criteriawhich is finely optimized for each unit of recording (e.g., sector orECC block), depending on the type of the data to be recorded in eachunit of recording. That is, even when different types of data, e.g.,audio or video data, and computer data, are both recorded on the samedisk, since the host device sends the criteria control information inassociation with the data to be recorded, and the defect management canbe effected using the optimum criteria for the respective data.

The control information specifying the criteria may select one of aplurality of criteria.

With the above configuration, the amount of control information issmall, since it only needs to specify one of the plurality ofpredetermined criteria, rather than specifying values forming thecriteria itself.

Data may be recorded in units of recording, and said method may furtherinclude recording control information representing the criteria for eachunit of recording, on the optical disk, in association with each unit ofrecording.

With the above configuration, the criteria to be used for defectdetection for each unit of recording (sector or ECC block) is known byreading the control information, and can be used for performingmaintenance of the data recorded on the disk.

According to a second aspect of the invention, there is provided a diskdevice for accessing data on an optical disk, including:

means for determining a criteria for detecting defects according to thetype of data for which defects are to be recorded; and

means for detecting defects using the criteria when data is recorded onor reproduced from the disk.

With the above arrangement, it is possible to use the criteria suitablefor the particular type of data for which defects are to be recorded.

The detecting means may detect said defects with regard to data recordedon the disk.

In this case the defects may be detected when the data is recorded onthe disk, or when the data is reproduced for verification of the datahaving been recorded. When the defects are detected as the data isrecorded, servo defects and header defects can be detected, but datadefects cannot be detected. When the defects are detected duringreproduction for verification, data defects as well as servo defects andheader defects can be detected.

The detecting means may alternatively detect defects when the data isreproduced. In such a case, if defects are detected, the reproduction ofthe data is re-tried. Decision on whether the reproduction is to bere-tried is made using different criteria depending on the type of databeing reproduced.

The device may comprise means for managing defects on the optical diskby using non-defective areas of the optical disk in place of defectiveareas.

With the above arrangement, the result of the defect detection can beused in making a decision as to whether the areas found to be defectiveshould be replaced with non-defective areas.

The determining means may include:

means for storing a plurality of criteria; and

means for selecting one of said plurality of criteria according to thetype of data for which defects are to be detected.

With the above arrangement, the defect criteria can be determined simplyby applying a signal for selecting one of the plurality of criteriaprovided in advance, rather than specifying the values forming thecriteria.

The plurality of criteria may include at least a first criteria, and asecond criteria, the second criteria being less strict than the firstcriteria, and the selecting means may select the first criteria when thedata for which defects are to be detected is one for which timerestriction with regard to data recording or reproduction is lessstrict, and selects the second criteria when the data for which defectsare to be recorded is one for which time restriction with regard to datarecording or reproduction is more strict.

An example of the data for which time restriction with regard to datarecording or reproduction is less strict is computer data. An example ofthe data for which time restriction with regard to data recording orreproduction is more strict is audio or video data.

By using a less strict criteria for the audio or video data,interruption of the audio or video data recording is avoided unless thedefect is of such a degree that the resultant sound or picture isintolerable.

The determining means may determine the criteria according to a controlsignal supplied from outside of the device.

The control signal may be supplied from a host device connected to thedisk device.

With the above configuration, the host device can set criteria which isfinely optimized for the type or contents of the data for which defectsare to be detected.

The device may further comprise means for recording data, in units ofrecording, on the disk,

wherein

said determining means may determine the criteria for each of the unitsof recording, and

the recording means may also record criteria control informationcontrolling the criteria for each unit of recording, in association withthe each unit of recording.

With the above configuration, the criteria to be used for defectdetection for the data of each unit of recording (e.g., sector or ECCblock) is known by reading the control information, and can be used forperforming maintenance of the data recorded on the disk.

According to a third aspect of the invention, there is provided anoptical disk for recording data, including an area storing criteriacontrol information specifying criteria to be used for detecting defectsfor data recorded on or reproduced from the disk.

With the above configuration, the criteria to be used for detectingdefects when the disk is accessed is known by reading the criteriacontrol information recorded on the disk. Accordingly, the maintenanceof the data on the disk is facilitated, and the interchangeability ofthe disk is improved since the criteria control information can be readby any disk device.

The data may be recorded in units of recording, and the criteria controlinformation indicating the criteria to be used for detecting detect withregard to the each unit of recording may be recorded in association withthe each unit of recording.

With the above configuration, the criteria to be used for each unit ofrecording, e.g., sector or ECC block, is known by reading the criteriacontrol information, and can be used for performing maintenance of thedata recorded on the disk.

The information may select said criteria from a plurality ofpredetermined criteria.

With this configuration, the amount of control information is small,since it only needs to specify one of the plurality of predeterminedcriteria, rather than specifying values forming the criteria itself.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram of an optical disk device of an embodiment ofthe present invention;

FIG. 2 is a block diagram of a defect determining means used in theoptical disk device of FIG. 1;

FIG. 3A is a schematic diagram showing examples of deformation of agroove forming a track;

FIG. 3B is a time chart showing a tracking signal obtained when thelight spot follows the track shown in FIG. 3A;

FIG. 4A is a diagram showing the configuration of a sector on a DVD-RAM;

FIG. 4B is a schematic diagram showing the signal obtained when thelight spot follows the sector shown in FIG. 4A;

FIG. 5 is a diagram showing an example of errors in an error correctingblock;

FIG. 6 is a table summarizing two sets of defect criteria;

FIG. 7 is a table summarizing three sets of defect criteria;

FIG. 8 is a block diagram of a defect determining means of anotherembodiment;

FIG. 9 is a diagram showing an example of procedure followed for settingdefect criteria;

FIG. 10 is a diagram showing another example of procedure followed forsetting defect criteria;

FIG. 11 is a diagram showing the configuration of an example of defectcriteria control information; and

FIG. 12 is a view showing arrangement of information for controllingdefect criteria on an optical disk.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention will now be described with reference to theattached drawings, in which like parts are indicated by like referencecharacters.

FIG. 1 is a block diagram of an optical disk device used to implementthe defect management method according to the invention. A disk rotatingmeans 4 controls rotation of an optical disk 2 for recording andreproducing data. An optical head servo means 22 performs positioncontrol over an optical head 6 such that a light spot formed by a lightbeam focused by the optical head 6 follows the track on the disk 2.

The light reflected from the optical disk 2 representing the datarecorded on the disk 2 is converted in the optical head 6 into anelectrical signal, which is supplied to an address reproducing means 8and a signal reproducing means 10. Based on an ID signal in the header,the address reproducing means 8 reproduces the address of a sectorcurrently accessed. The detected address is sent to a drive controlmeans 14. The signal reproducing means 10 reproduces signals from thesignals supplied from the optical head 6 in accordance with therecording format. A data reproducing means 16 corrects errors in thereproduced signals to produce information, and outputs information to ahost device (not shown) as reproduced data of the desired logical block.

At that moment, the data reproducing means 16 can recognize a sector inwhich the required data is recorded on the basis of control signalsreceived from the drive control means 14. Concurrently, the drivecontrol means 14 sends a command to control the rotational speed of thedisk 2, to the disk rotating means 4. Further, the drive control means14 determines the position on the disk, of the sector containing theinformation to be reproduced, and sends commands to the optical headaccess means 20 for moving the optical head 6 to the position of thesector. The drive control means 14 also sends commands to control theoperation of the servo system. The optical head access means 20 and theoptical head servo means 22 control the position of the optical head 6in accordance with the received commands.

A defect management control information detecting means 18 reads controlinformation necessary for performing defect management, from thereproduced data, and obtains information concerning defect managementsuch as defect management method applied to the disk, arrangement ofspare areas and user areas, status of use of substitutive sectors, anddefect criteria. The information thus obtained is sent to the drivecontrol means 14 and used for controlling devices engaged in defectmanagement at the time of recording or reproducing data.

Incidentally, all the sectors on the disk are numbered with consecutiveaddresses from the inner or outer periphery of the disk. However, theaddresses of user data recording sectors are not consecutive. This isbecause the physical addresses are assigned not only to the user datarecording sectors, but also to sectors in spare areas provided fordefect replacement and sectors in guard areas at zone boundaries in thecase of a zone format disk.

At the time of performing access from the host device through aninterface, logical block numbers of a file system are used. Therefore,the disk device needs to perform conversion between a logical blocknumber and a sector address. The conversion is carried out by the drivecontrol means 14 in accordance with received information on defectmanagement.

In writing operation, data sent from the host device is first inputtedto a data recording means 24. The data recording means 24 performs errorcorrection coding on the data in accordance with a format, and outputsthe data as signals to be recorded, with timings controlled inaccordance with the sector addresses on the disk, having been detectedby the control signals supplied from the drive control means 14.

A signal recording means 26 modulates the received signals in accordancewith a recording format and sends them to the optical head 6.

The optical head 6 writes the signals into the optical disk 2 by drivinga laser.

At this moment, the optical head 6 is controlled such that a light spottraces the sector the data is to be recorded, by means of the opticalhead access means 20 and the optical head servo means 22.

The drive control means 14 stores defect management control informationdetected by the defect management control information detecting means 18at the time of disk loading. The logical block number of the block to beaccessed is given by an interface control signal supplied from the hostdevice, not shown. To be more specific, the host device sends arecording command specifying the logical block number of the block wherethe data is to be written, and the like, to the disk device, togetherwith the data to be recorded, or sends a reproducing command specifyingthe logical block number of the block from which the data is to be readand the like, to the disk device.

The drive control means 14 converts the logical block number of theblock to be accessed, to physical addresses, using defect managementinformation, and sends a command specifying the physical addresses ofthe sectors to be accessed, to the optical head access means 20 and datarecording means 24 or data reproducing means 16. The physical addressesof the sectors currently accessed are reproduced by the addressreproducing means 8, and inputted to the drive control means 14. Drivecontrol operations such as control over the optical head access means 20and data recording means 24 or data reproducing means 16 are performedon the basis of the detected current address and the target address.

A defect determining means 12 makes judgment as to whether a sector isdefective and is to be replaced. The defect determining means 12receives information necessary for defect determination on each sectorfrom the optical head servo means 22, address reproducing means 8, anddata reproducing means 16, and determines presence or absence of adefect in accordance with a defect criteria set by the drive controlmeans 14, and reports the results of the determination to the drivecontrol means 14. When the sector having been accessed is determined asa defective sector, the drive control means 14 performs the necessaryprocesses. During recording, the drive control means 14 interrupts therecording operation and causes the data of the block to be re-recordedin substitutive sectors. During verifying reproduction, the drivecontrol means 14 causes the data of the block having been recorded, tobe re-recorded in substitutive sectors. During reproduction, the drivecontrol means 14 causes the reproduction to be re-tried. Theseoperations are pre-programmed into the drive control means 14.

FIG. 2 shows the configuration of the defect determining means 12. Itreceives servo error signals such as a tracking error signal and a focuserror signal from the optical head servo means 22. It also receives aheader error signal representing the number of errors in ID's reproducedfor each sector, from the address reproducing means 8. It also receivesa data error signal representing the number of errors in the reproduceddata from the data reproducing means 16.

In this embodiment, the defect determining means 12 includes two defectcriteria storing means 34 and 36 for storing different defect criteria Aand B, respectively. The two defect criteria A and B are inputted to adefect criteria selecting means 38, which selects and outputs either oneof the two criteria A and B in accordance with a defect criteria settingsignal CS. There are three outputs, Rs, Rd, and Rh. A reference signalRs for detecting a servo defect is inputted to a servo defect detectingmeans 28, a reference signal Rh for detecting a header defect isinputted to a header defect detecting means 32, and a reference signalRd for detecting a data defect is inputted to a data defect detectingmeans 30. They are compared with a servo error signal Es, a header errorsignal Eh, and a data error signal Ed in the respective defect detectingmeans 28, 32 and 30, to detect presence or absence of a servo defect, aheader defect, and a data defect. A defect detecting means 40 receivesthe outputs of the defect detecting means 28, 3l and 30, and outputs adefect detection signal DF when at least one of the defects has beendetected.

Referring to FIG. 3A and FIG. 3B, detection of a servo defect will bedescribed. For recording data, a track which has a substantially uniformwidth Wt (the track is actually circular or spiral, but the short partof the track illustrated can be treated as straight) is used. The trackis formed of a continuous guide groove or the like. Consideration willbe given to the case where the track is deformed at points X and Y. Suchdeformation may be caused due to dirt introduced during fabrication of amaster disk or a substrate, irregular operation of a manufacturingmachine, unevenness of a formed substrate, and other minorirregularities. Tracking control is performed such that a light spotfollows the centerline 42 c of the track shown by a chain line in FIG.3A, and a tracking error signal Et shown in FIG. 3B is obtained. Thetracking error signal Et is zero when the light spot is following thecenterline 42 c of the track. When the light spot deviates from thecenterline 42 c, the tracking error signal Et deflects either positivelyor negatively depending on the direction and the amount of deviation.Where there is a deformation of the track and the centerline 42 c of thetrack is bent abruptly, since the light spot cannot follow the abruptbending, the light spot deviates from the centerline 42 c.

At point X, there is a deflection in the tracking error signal Et due tothe deformation of the track. At point Y, there is also a deflection inthe tracking error signal Et due to meander of the track. If thetracking error tolerance limit Rtb shown by the broken line in FIG. 3Bis given as a reference for determining a servo defect, a servo defectis recognized at point Y. If a more strict tracking error tolerancelimit Rta shown by the chain line in the figure is given, servo defectsare recognized both at points X and Y.

The tracking error tolerance limit Rta corresponds to the value of thetracking signal Et when the deviation of the light spot is one-fourththe tracking width Wt, and the tracking error tolerance limit Rtbcorresponds to the value of the tracking signal Et when the deviation ofthe light spot is one-eighth the tracking width Wt.

For instance, if the level Rta at the chain line is used as the defectcriteria A, and the level Rtb at the broken line the figure is given asthe defect criteria B, it is possible to perform servo defectdetermining process at two different levels. Incidentally, the recordingtrack may not be a continuous groove. In a disk, such as a DVD-RAM,where user data recording areas are formed of lands and grooves, and nogroove is formed at the header parts, which are formed of pre-pits only,it is sufficient to perform a servo defect detection only for areaswhere a groove continues.

Servo defect detection can be performed with regard to a focus errorsignal, in the same way as the tracking error signal.

FIG. 4A shows the configuration of a sector in a groove track in aDVD-RAM, and FIG. 4B shows the waveform of the signal reproduced fromthe sector shown in FIG. 4A. These drawings will be used for describingthe detection of header defect. A recording sector of a DVD-RAM includesa header area having a sector address and the like at the beginning,followed by a data area for recording user data. The header areaincludes four ID's, indicated as ID1 to ID4 each containing addressinformation representing a sector address. In the sector shown in FIG.4A, ID1 and ID2 are displaced one-half the track width Wt toward theouter periphery of the disk, and are shared with a sector in the outeradjacent land track, while ID3 and ID4 are displaced one-half the trackwidth Wt toward the inner periphery of the disk, and are shared with asector in the inner adjacent land track.

In a land track not shown, ID1 and ID2 are displaced by one-half thetrack width Wt toward the inner periphery of the disk, and are sharedwith a sector in the inner adjacent groove track, and ID3 and ID4 aredisplaced by one-half the track width Wt toward the outer periphery ofthe disk, and are shared with a sector in the outer adjacent groovetrack. The waveform of the signal reproduced from the header area andthe data area in a sector in a land track is also shown in FIG. 4B.

The data area following the header is in a groove or a land, andcontains a synchronous signal (SYNC), control information (CI), userdata, and an error-correcting codes, and a buffer, which are recordedsuccessively in this order. The control information CI consists of asmall amount of information (such as the data number of the sector),other than user data.

The size of user data, together with the control information, in onesector is 2 KB (kilobytes), and error-correcting coding is performedtaking the user data and the control information of 32 KB in 16successive sectors, as a unit, wherein error-correcting codes are addedto the to form an ECC block.

The error-correcting codes are distributed over the 16 sectors.

The sector address can be obtained if even one of the four ID's in aheader is read correctly. In criteria B, if none of the four ID's isread correctly, the sector is found have a header defect, and if two ormore sectors within an ECC block are found to have a header defect, theECC block is found to have a header defect. In criteria A, if not morethan one of the four ID's is read correctly, the sector is found have aheader defect, and if one or more sectors within an ECC block are foundto have a header defect, the ECC block is found to have a header defect.

A sector found to be non-defective according to criteria A has at leasttwo correctly readable ID's. This make it more likely that at least oneID will remain correctly readable even if the disk is later soiled ordegraded, or transferred to another disk device.

In this way, it is possible to perform header defect determination withtwo different levels.

FIG. 5 shows the structure of an ECC block in a DVD-RAM. This drawing isused to describe the data defect detection. In the data recording means24, the 23 KB data for 16 sectors are arranged in the form of matrix of172 bytes in the row direction by 192 bytes in the column direction. A16-byte parity outer code PO in the column direction is added to eachcolumn, and then 10-byte parity inner code PI in the row direction isadded to each row.

Thus, a product code, which is a Reed-Solomon code, of 182 bytes×208bytes is formed.

When the data is recorded on the optical disk 2, the PO rows areinterleaved with the other rows so that the error-correcting code bytesare evenly distributed over all 16 sectors of the ECC block.

At the time of reproduction, the data reproducing means 16 rearrangesthe reproduced signal into a matrix of 182 bytes×208 bytes, and firstdetect and correct any errors of each row by means of the 10-byte innercode PI. The inner code PI is capable of correcting errors in up to fivebytes per row, and detecting errors in up to ten bytes per row.

Next the 16-byte outer code PO is used to detect and correct anyremaining errors. The outer code PO is capable of correcting errors inup to 8 bytes per column, and detecting errors in up to 16 bytes percolumn. These error detecting and correcting capabilities can beimproved by repeating the PI-PO error correction process, although theadditional repetitions require additional circuitry and additional time.

When a large number of errors are detected and corrected, it becomeslikely that some of the corrections are wrong, the corrected datadiffering from the original data. Criteria A and B are therefore set,for example, as follows. In criteria A, a row is considered to have adata defect if errors are detected in at least four bytes, which isclose to the error-correcting limit of the PI code, and an ECC block isconsidered to have a data defect if it has at least eight rows having adata defect. In less strict criteria B, a row is considered to have adata defect if errors are detected in at least eight bytes, which isclose to the repeated error-correcting limit of the PI code, and an ECCblock is considered defective if it has at least eight rows having adata defect. When an ECC block is considered to have a data defect, allsixteen of its constituent sectors are replaced.

In this way, it is possible to perform data defect determination withtwo different levels.

In FIG. 5, row three has errors in four bytes, indicated by x's. Thisrow is deemed to have a data defect under criteria A, but not undercriteria B.

In this way, the presence or absence of defect in each sector can bedetermined with respect to each of the servo defect, the header defect,and the data defect, according to the defect criteria supplied to eachdefect detecting means. FIG. 6 summarizes the defect criteria A and Bdescribed above described as examples for the respective defects. Theset of criteria A are stored in the criteria storing means 34, while theset of criteria B are stored in the criteria storing means 36. It isthen possible to switch between the two levels of criteria A and B bymeans of the criteria selecting means 38, according to the criteriasetting signal Cs.

In the case of recording computer data, a high reliability is requiredso that the data once recorded are not lost or changed. For this reason,verifying reproduction is often effected at the time of recording.Accordingly, during recording and during verification production, thestrict criteria A is applied to ensure that the correct data isrecorded.

In contrast, in the case of audio or video data, continuous recording ata high transfer rate is required. Accordingly, verifying reproduction isoften omitted, ignoring data defects. Even if some defects occur duringrecording, as long as occurrence of the defects is of such a degree thatthe defects can be corrected or concealed later at the time ofreproduction, it is preferable to continue recording operation ignoringthe defects, since it will improve the performance and the operabilityas a recorder. For this reason, the criteria set for servo defects andheader defects are set at a less strict level at which the recorded datacan be corrected or concealed.

When the two different defect criteria A and B available, the strictcriteria A is used for recording computer data, while the less strictcriteria B is used for recording audio or video data.

There are situations where more than two different levels of reliabilityare required depending on types of data to be recorded. For instance,there is a situation where three different levels are required, one forrecording computer data, another for recording important audio or videodata, and the last one for recording normal audio or video data. In sucha situation, as shown in FIG. 7, provision is made to enable switchingamong three different defect criteria A, B, and C. Criteria A and B arethe same as those described with reference to FIG. 6, and are used forrecording computer data and for recording normal audio or video data,respectively.

The criteria C is used for recording important audio or video data, andtherefore, it has strictness intermediate between the criteria A and B.In the criteria C, the allowable deviation in tracking error isone-sixth the track width Wt, and an ECC block is found to have a headerdefect if all four ID's are unreadable in any one sector. Regarding datadefects, criteria C and A are the same.

To use the three different sets of defect criteria, the defectdetermining means 12 should have an additional criteria storing means,in addition to the members shown in FIG. 2, and the criteria selectingmeans 38 should be able to select among the criteria A, B and C suppliedfrom the above-mentioned additional criteria storing means, as well asthe criteria storing means 34 and 36 in FIG. 2, in accordance with thecriteria setting signal CS.

FIG. 8 shows another embodiment of the defect determining means 12. Theconfiguration of FIG. 8 is different from the configuration of FIG. 2 inthat the criteria storing means 34 and 36, and the criteria selectingmeans 38 which makes selection according to the criteria selectingsignal CS shown in FIG. 2 are replaced with a defect setting and storingmeans 46 which makes setting according to the criteria selecting signalCS.

The defect criteria to be applied is supplied from a host device (notshown) through an interface to the drive control means 14. In response,the drive control means 14 generates a criteria setting signal CSspecifying the criteria.

In the defect determining means 12 of FIG. 2, the defect criteria storedin the respective criteria storing means are fixed. However, inpractical use, it may be desirable that the host device which controlsthe disk device (recording device) can flexibly vary the criteria so asto optimize the reliability and the transfer rate, depending on thenature, type, characteristics, and the degree of importance of the datato be recorded. For instance, a countermeasure for errors may beprovided in the application software or file system. That is, errorcorrecting coding may be applied before transmitting the data to thedisk device at a predetermined rate. In this case, the defect managementat the disk device is not so important, and the capability of continuousreal-time recording at a high data transfer rate may be important.

The embodiment described above can meet with these requirements.

An embodiment of procedure followed in setting a defect criteria will bedescribed with reference to FIG. 9. First, the host device sets thedefect criteria to be used, according to type or contents of the data tobe recorded. Then, a command for setting the criteria is sent from thehost device to the disk device (drive). The disk device selects or setsthe criteria upon reception of the command accordingly. In the systemshown in FIG. 2, the command sent from the host device to the diskdevice is one for merely specifying selection between the criteria A andB. In the system shown in FIG. 8 in which the defect criteria can beset, the system is so configured that the defect criteria can be setarbitrarily at the host device, and the command indicates the defectcriteria set at the host device. Details of the command for setting thedefect criteria may be one. which will be described later with referenceto FIG. 11, in which the defect criteria control information can selectone among a plurality of criteria independently, for each of the servodefect, header defect, and data defect.

The host device then sends a recording command together with the data tobe recorded. Upon reception of the command, the disk device records datain the specified sectors, and performs the defect management using thedefect criteria set in the manner described above, and reports theresults of the defect management to the host device. The host deviceterminates a series of recording when it confirms that recording hasbeen completed correctly. If the recording has been done incorrectly, apredetermined process (re-writing or informing the user) for dealingwith the incorrectness is carried out.

According to the procedure of FIG. 9, the host device, which knows thecontents of the data to be recorded, sets the defect criteria finelyoptimized according to the type or contents of the data. It is thereforepossible to provide flexibility for obtaining an optimum combination ofreliability and transfer rate according to the intended use of the data.

FIG. 10 shows another embodiment of a procedure followed for setting adefect criteria. In this embodiment, a command which sets a defectcriteria and also instructs data recording is sent. First, the hostdevice determines a defect criteria to be used in accordance with thetype or contents of the data to be recorded, and then prepares the datato be recorded. This order may be reversed.

Then, the host device sends the recording command which also sets thedefect criteria, to the disk device. In accordance with the designateddefect criteria, the disk device selects or sets the criteria. Thedesignation of the setting sent from the host device to the disk devicemay be one for specifying selection among a plurality of preset criteria(such as between the criteria A and B), or one for setting an arbitrarycriteria.

The disk device records the data received together with the command, onthe disk, while performing defect management in accordance with thedefect criteria which has been set as described above, and informs thehost device of the result. According to this embodiment, it is possibleto obtain an optimum combination of reliability and transfer ratedepending on the intended use of the disk, as in other embodimentsdescribed earlier. Moreover, because the number of commands transferredis reduced, the overhead is reduced, and the possibility of the transferrate becoming lowered is reduced.

A manner of recording control information representing the defectcriteria designated at the time of data recording, in every sector on adisk will now be described. FIG. 11 shows the configuration of a defectcriteria control information. With this configuration, one of fourdifferent criteria can be specified for each of the servo defect, theheader defect and the data defect independently, by using one byte.

The most-significant bit b7 indicates the mode of designation of thedefect criteria. If the value of bit b7 is “1”, the mode designated byother bits of the control information byte is used, while if the valueis “0” the default criteria which the disk device has is used ignoringthe other bits of the control information byte.

The next bit b6 indicates the range within which the defect criteriashould be applied. If the value of bit b6 is “1”, the mode set by otherbits in the control information byte of are applied for each unit ofrecording, e.g., each sector or block. If the value of bit b6 is “0” thesame criteria is to be applied over the entire surface of the disk.

The next two bits (b5 and b4) indicate the criteria applied for theservo defect, among the four criteria. If the combined value of bits b5and b4 are “11” the tracking error tolerance above which the servodefect is recognized is one-forth the track width Wt. If the combinedvalue is “10” the tolerance is one-sixth the track width Wt. If thecombined value is “0” the tolerance is one-eighth the track width Wt. Ifthe combined value is “00” the tolerance is one-tenth the track widthWt.

The next two bits b3 and b2 indicate the defect criteria to be appliedfor the header defect, among the four criteria. If the combined value ofthe bits b3 and b2 is “11” the ECC block is found to have a headerdefect if all four ID's are unreadable at two or more of its sectors. Ifthe combined value is “10” the ECC block is found to have a headerdefect if three or more ID's are unreadable at two or more of itssectors. If the combined value is “01” the ECC block is found to have aheader defect if all four ID's are unreadable at one or more of itssectors. If the combined value is “00” the ECC block is found to have aheader defect if three or more ID's are unreadable at one or more of itssectors.

The last two bits b1 and b0 indicate the defect criteria to be appliedfor the data defect, among the four criteria. If the combined value ofthe bits b1 and b0 is “11”, the ECC block is found to have a data defectif at least 16 of its rows have errors in at least 8 bytes each. If thecombined value is “10”, the ECC block is found to have a data defect ifat least 8 of its rows have errors in at least 8 bytes each. If thecombined value is “01”, the ECC block is found to have a data defect ifat least 8 of its rows have errors in at least 4 bytes each. If thecombined value “00”, the ECC block is found to have a data defect if atleast 6 of its rows have errors in at least 4 bytes each.

The above described defect criteria control information can be locatedin each sector which constitutes a minimum unit of recording. In aDVD-RAM, a one-byte area may be reserved in the control information arealocated at the beginning of the data area shown in FIG. 4. The criteriamay be set for each sector separately. The same defect criteria controlinformation may be set in all the sectors within the same ECC block, orin predetermined sectors, so that the defect criteria controlinformation is repeatedly recorded, and the range within which the samedefect criteria should be applied may be made to coincide with the unitof error correction (ECC block).

The provision for enabling setting the finely optimized criteriaimproves the utility for the user in multimedia applications in whichthe audio or video data and computer data are intermixed with eachother. It should be noted that the defect criteria to be applied to therespective data can be switched at the system (host device) depending onthe contents of the data, and it is possible to realize a flexibilityfor obtaining the optimum combination of the reliability and transferrate.

It is possible to pre-select a defect criteria to be used in recordingon a disk, and record the criteria as defect criteria controlinformation on the disk, before the disk is used. FIG. 12 shows anexample of arrangement of control information areas, and a datarecording region including user areas and spare areas, and arrangementof defect criteria control information in the control areas. The datarecording region is divided into groups, each of which includes a userarea and a spare area. The control information areas are disposed nearthe inner and outer peripheries of the disk, and the same controlinformation is recorded on the respective control information areas.

In a known example, a defect management method is recorded in a controlinformation area. In contrast, according to this embodiment, defectcriteria control information is stored in a control information area. Atthe time of starting a disk, the disk device reads the defect criteriacontrol information to know the defect criteria. If the defect criteriasuitable for the intended use, such as computer data, audio or videodata, or the like is recorded, the defect determination according to thedefect criteria can be made.

If one bit is provided in the control information area for recording thedefect criteria control information, it is possible to record two setsof defect criteria, and selectively use them. For recording three orfour sets of defect criteria, and using them selectively, two bitsshould be provided in the control information area. If one byte isprovided in the control information area, it is possible to select oneof the criteria for each of the servo defect, data defect and headerdefect, and to specify a combination of specific defect criteria for therespective types, as described with reference to FIG. 11.

With such a provision, if the information is recorded once at the timeof initialization of the disk, the defect criteria can be applied to allthe data thereafter recorded on the disk. It is therefore possible toeliminate to need to set the defect criteria each time the data isrecorded. Accordingly, the recording can be effected at a high speed,and in a simple manner.

What is claimed is:
 1. A method of managing defects on an optical diskused for recording data, comprising: determining criteria for detectingdefects according to the type of data for which defects are to bedetected; and, detecting defects using said criteria when data isrecorded on or reproduced from said disk, said method further comprisingsending control information for specifying said criteria, from means forprocessing data to be recorded, to means for recording said data.
 2. Themethod according to claim 1, wherein data is recorded in units ofrecording, and said step of sending control information sends thecontrol information for each unit of recording.
 3. The method accordingto claim 1, wherein said control information specifying said criteria isfor selecting one of a plurality of criteria.
 4. A disk device foraccessing data on an optical disk, comprising: means for determiningcriteria for detecting defects according to the type of data for whichdefects are to be detected; and means for detecting defects using saidcriteria when data is recorded on or reproduced from said disk, whereinsaid determining means determines the criteria according to a controlsignal supplied from outside of the device.